1. Field of the Invention
The present invention relates to a disk drive in which when an error is detected in a signal read from a disk, a retry operation is performed for rereading the same signal from the disk.
2. Description of the Related Art
A signal read from a disk, which is loaded in a hard disk drive, using heads contains an error checking code. The error checking code is used to check or correct a read signal for an error. If an error occurs in a signal read using the heads or an error value is equal to or larger than a predetermined value, a retry operation is performed for rereading the same signal from the disk.
The retry operation is generally performed based on a table like Table 1.
The left column of Table 1 indicates retry numbers, and the right column thereof describes the contents of correction. For example, the first retry operation, a magnitude off-track by which the heads come off from a track on the disk is set to +10%. For the second retry operation, the magnitude of off-track is set to xe2x88x9210%. For the third retry operation, the cutoff frequency of a low-pass filter is changed by xe2x88x9210%. Moreover, the capacitances of RHP and LHP boost capacitors stored in registers determines a response time required by the low-pass filter. The asymmetry of the signal read using the head varies depending on the capacitances of the RHP and LHP boost capacitors.
A retry is carried out a predetermined times according to the table like Table 1. If an error rate does not fall below a predetermined value through the predetermined number of retries, the retry operation is suspended. The signal read using the heads is ranked as an unreadable signal.
However, as far as the retry operation based on the table like Table 1 is concerned, the probability at which the error rate may is converged owing to the retry operation is low. Moreover, when many parameters are specified as the conditions for reading, the number of necessary retries indicated in the table like Table 1 becomes very large.
For hard disk drives, the quality of disks is managed carefully and the disks are of the same kind. Moreover, a change in the relative position of a disk with respect to heads or a change in a use environment can be predicted. As shown in Table 1, the number of parameters that should be varied for each retry operation is relatively small.
However, when different kinds of disks including a flexible magnetic disk for high-density recording are loaded in a disk drive, individual disks are different from one another in terms of quality. Moreover, the individual disks are different from one another in terms of how a signal is recorded. For using this kind of disk in combination with a disk drive, consideration must be taken into the compatibility of a disk with a disk drive. Moreover, such factors of a use environment as temperature, humidity, and voltage are variable. For example, assume that the number of parameters that should be varied for each retry is five and each parameter is varied in five steps. In this case, the number of settings of conditions for reading is 3125 or the fifth power of 5. If all the variable parameters were listed as a table like Table 1, the number of retries would be very large. It would take along time to complete a retry operation.
Moreover, if the number of parameters and the number steps in which the parameters are varied were made smaller, the probability that an error detected in a read signal can be repaired would be lowered.
By the way, test data is written or read in or from the flexible magnetic disk for high-density recording during a quality test to be conducted after completion of manufacturing. At this time, if data cannot be read normally, the same retry operation as the foregoing one is carried out. If an error rate at which an error is detected in a read signal does not fall below a predetermined value through a predetermined number of retry operations, a sector concerned is judged as a defective sector. The sector number of the sector is registered as that of a defective sector in a maintenance area on a magnetic disk.
When this kind of magnetic disk is loaded in a normal disk drive, the maintenance area is read first. The defective sector number is identified, and the defective sector will not be used for recording.
However, even when a sector of a disk has not been registered as a defective sector during a quality test, the disk may presumably be flawed during a normal use after delivery. Otherwise, dust may be interposed between a disk and a head. This raises an error rate at which an error occurs in reading a signal. Consequently, while data is being reproduced from a sector that has not been registered as a defective sector in the maintenance area on a disk, it may be requested to carry out a retry operation with various parameters varied as mentioned above. At this time, unless the various parameters are optimized and a retry is carried out, the probability that the error may not be able to be repaired gets higher.
The present invention attempts to overcome the foregoing drawbacks of related arts. An object of the present invention is to provide a disk drive capable of acquiring a normal read signal or a read signal whose error can be corrected by performing the smallest number of retries according to a so-called fast diving method. According to the fast diving method, parameters are set based on change values by which parameter values are changed for each retry operation and the magnitude of a change in an error value in data read during a retry, so that the error value can be converged.
Another object of the present invention is to provide a disk drive capable of identifying a sector, which cannot be recovered by performing a retry, as a defective sector. At the time of a quality test to be conducted before delivery of a disk, a retry is performed under severe conditions than it is performed on a disk used by a user. Thus, the disk drive has decreased the frequency of occurrence by which a retry occurs during use of a disk by a user.
According to the present invention, there is provided a disk drive in which a signal recorded on a disk is read using heads and in which when an error is detected in the read signal, a retry operation is performed for rereading the same signal recorded on the disk. The disk drive includes an error detection unit, a memory, and a control unit. The error detection unit detects an error value in a signal read using the heads. A set value of a parameter concerning the relative position of the heads with respect to a disk attained at the time of reading the signal and/or a set value of a parameter concerning a circuit for processing the signal read using the heads is stored in the memory. When the control unit judges from an error value in a signal read using the heads that a retry is needed, the control unit changes the parameter value by a predetermined value and instructs rereading of the signal. Moreover, the control unit calculates a new parameter value according to a change value by which the parameter value is changed and a change in an error value detected in a reread signal. The control unit updates the parameter value stored in the memory with the new parameter value. If rereading is still needed, the new parameter value is changed by the predetermined value and the signal is reread. Another new parameter value is calculated and the stored parameter value is updated with the new parameter value. The control unit repeats this retry operation until the error is eliminated, until the error value falls below a predefined value, or until the number of retries reaches a predetermined number of retries.
For example, a change value xcex2 by which a parameter value is changed for each retry operation and a coefficient of update xcex1 are predetermined. Assuming that the parameter value stored in the memory is P, the parameter value P is changed by the change value xcex2 and the signal is reread during the retry operation. If the magnitude of a change in an error value is xcex4E, Pxe2x80x2=Pxe2x88x92xcex1xc2x7(xcex4E/xcex2) is solved. Pxe2x80x2 is regarded as a new parameter value with which-the contents-of the memory are updated.
In other words, when any parameter value is changed by a predetermined value for each retry, a parameter value to be set for the next retry is calculated based on the magnitude of a change in an error and the change value by which the parameter value is changed. Consequently, the error value can be gradually converged to zero with the progress of repetition of a retry. Thus, an error can be repaired by performing a small number of retries.
Moreover, a maintenance area in which a defective sector is registered during a disk test is defined on a magnetic disk. A table listing parameter values stepwise is used for the disk test. When an error value detected in a recorded signal is equal to or larger than a predetermined value, a retry operation based on the table is repeated a predetermined number of times. When the error value does not fall below the predetermined value through the predetermined number of retries, a sector concerned is regarded as a defective sector. The detective sector is preferably registered in the maintenance area.
As part of a quality test to be conducted prior to delivery of a disk, a retry is carried out according to the table method described in conjunction with the related art. A sector that cannot be recovered from an error is registered as a defective sector in the maintenance area on a disk.
When the disk is loaded in a user""s disk drive, a retry operation is performed based on the setting of a parameter determined using the aforesaid arithmetic operation. Even when a sector of a disk is not registered as a defective sector at the time of a quality test, if the disk is flawed after delivery, an error rate at which an error is detected in a signal read from the sector is high. Nevertheless, once a retry is carried out using the arithmetic operation, the probability of succeeding in repairing an error can be raised.